In the field of welding aluminum alloys, it is known that the growth of coarse grains is detrimental because it can cause cracks and “hot tearing.” One of the methods for preventing the growth of coarse grains is the addition of zirconium or titanium to the filler wire (welding wire). A typical filler wire for welding aluminum alloy parts is an aluminum alloy wire with a diameter typically between 0.8 and 3.2 mm, which contains the chemical elements to be provided in the welded joint. In this context, the base of the alloy of the wire, which is chosen for its metallurgical compatibility with the products to be welded, should be distinguished from additives the role of which is to modify the solidification structure of the welded joint. The base of the alloy of the filler wire must make it possible to obtain a welded area with high mechanical strength. But it is in particular the solidification of the welded joint that can cause defects, some of which will be immediately visible, while others appear only after a certain period of use of the welded construction.
For a given welding procedure, and on the condition that this procedure does not in itself cause welding defects (that it is therefore performed according to good practice), the influence of the chemical composition of the filler wire on certain properties of the weld bead can therefore be significant.
The article “Effects of grain refinement of aluminum weldability,” by M. J. Dvornal, R. H. Frost and D. L. Olson, published in Weldability of Materials, ASM International (1990), teaches that these additive elements are effective only if they are in the form of intermetallic phases of the TiAl3 or ZrAl3 type. U.S. Pat. No. 5,104,456 (Colorado School of Mines) describes a method for producing a filler wire that contains these phases with a controlled shape, morphology and particle size distribution.
The patent application EP 1 249 303 A1 (McCook Metals L.L.C.) describes an aluminum-based welding filler wire containing zirconium and/or titanium in a concentration greater than 0.25%, which can also contain the elements Sc, Hf, V, Mn, Cu, Fe and Si. This wire was developed for fusion welding of alloy AA2195 (Al—Cu—Li alloy).
In alloy AA2090 (also Al—Cu—Li type), it was noted that the addition of Ti, Zr or Ti+B to filler wires made of alloy 2319 or 4043 caused refinement of the grain in the welded area, which makes it possible to reduce hot cracking in the welding of parts made of alloy 2219. The best results are obtained with zirconium alone in an amount of around 0.18% as described in “Use of inoculants to refine weld solidification structure and improve weldability in type 2090 Al—Li alloy,” by G. D. Janaki Ram et al., published in the journal Materials Science and Engineering A276 (2000), p. 48-57.
The patent application EP 0 238 758 (Martin Marietta) describes a method for welding metal matrix composites in which the weld or the filler wire are prepared by in situ precipitation of a ceramic material in a metal matrix. In the case of an aluminum-TiB2 composite, the presence of free titanium is not encouraged because it can have a detrimental effect on the viscosity of the liquid metal for the casting operation.
In the field of aluminum alloy casting, the use of refining wires, aluminum alloy wires containing titanium additives, is also known. These wires are typically available in a diameter of 9.5 mm. A wire commonly used for refining aluminum alloys is an alloy containing 5% Ti and 1% B, which contains particles of TiB2 and free titanium. Free titanium, as used herein, refers to titanium not combined with boron, but possibly combined with aluminum in the form of Al3Ti.
The present disclosure is provided to solve the problem discussed above and other problems, and to provide advantages and aspects not provided by prior welding, filler wires and welding methods of this type. For example, the present disclosure provides welding filler wires that make it possible, by comparison with prior welding wires, to achieve better refining in the weld bead, i.e. a finer and more regular grain, and which simultaneously make it possible to obtain good mechanical strength in the welded joint.
A full discussion of the features and advantages of the present invention is deferred to the following detailed description.